Method for determining metallogenic potential of porphyry by using trace elements and b isotope of tourmaline

Abstract

In a method for determining metallogenic potential of a porphyry by using trace elements and a B isotope of tourmaline, redox properties of magma is determined with Fe 3+ /(Fe 2+ +Fe 3+ ) of tourmaline; then a water content and a content of metal Cu of the magma are determined with contents of H 2 O and Cu in the tourmaline; and a source of the magma is determined with a B isotope of the tourmaline, the water content, oxygen fugacity and metal content and source of the magma are finally determined, and finally, whether the magma has metallogenic potential of a porphyry is comprehensively determined. The present disclosure determines a key control factor of porphyry copper with a mineral of the tourmaline, and overcomes the difficulties in low efficiency, a long period and high cost of a traditional method for determining metallogenic potential.

What is claimed is: 
     
         1 . A method for determining metallogenic potential of a porphyry by using trace elements and a B isotope of tourmaline, comprising:
 S1, delineating a metallogenic section:   collecting geological data, geophysical data and geochemical data according to a selected research region, comprehensively analyzing a metallogenic prospect, and delineating a favorable metallogenic section;   S2, collecting samples:   collecting the samples from porphyries having metallogenic potential in the favorable metallogenic section, and picking out tourmaline in the samples;   S3, analyzing the tourmaline:   analyzing major elements of the tourmaline: observing features of the corresponding tourmaline under a microscope and a cathode luminescence image, recording petrographic features of the tourmaline in detail, analyzing contents of the major elements in the tourmaline in different regions by using an electron probe to obtain a molecular formula of the tourmaline, and determining a content of H 2 O in the tourmaline with the molecular formula of the tourmaline;   analyzing trace elements of the tourmaline: carrying out laser ablation inductively coupled plasma mass spectrometry in-situ micro-region element analysis on the tourmaline samples to obtain contents of the trace elements, comprising contents of Sr, Y and Cu elements, of the tourmaline of each test point; and   analyzing the B isotope of the tourmaline: carrying out multi-acceptance laser ablation inductively coupled plasma mass spectrometry in-situ B isotope analysis on the tourmaline samples to obtain δ 11 B isotope composition of each test point;   S4, determining metallogenic potential of the porphyry with oxygen fugacity, water content, and metal content and source:   wherein the oxygen fugacity is determined by: analyzing data obtained from analysis of the major elements, if a ratio of Fe 3+ /(Fe 2+ +Fe 3+ ) is less than 0.45 and a ratio of Mg/(Mg+Fe) is less than 0.5, it is indicated that the porphyries have no metallogenic potential of a porphyry, and otherwise, it is indicated that the porphyries containing the tourmaline have potential to form porphyry copper;   the water content is determined by: analyzing data obtained by analyzing the major element and analyzing the trace elements, if a content of H 2 O is less than 3.58 and a ratio of Sr/Y is less than 200, it is indicated that the porphyries have no metallogenic potential of a porphyry, and otherwise, it is indicated that the porphyries containing the tourmaline have the potential to form the porphyry copper;   the metal content is determined by: analyzing data obtained by analyzing the trace elements, if a content of Cu is less than 1.5 and a ratio of Sr/Y is less than 200, it is indicated that the porphyries have no metallogenic potential of a porphyry, and otherwise, it is indicated that the porphyries containing the tourmaline have a high content of Cu and have the potential to form the porphyry copper; and   the source is determined by: analyzing data obtained by analyzing the B isotope, if the tourmaline in the porphyries satisfies a content of δ 11 B being between −8.5 and −5 and a ratio of Sr/Y being lower than 200, it is indicated that the porphyries have a contribution of mantle-derived magma and have the potential to form a porphyry copper deposit;   if the porphyries is determined to have the high water content, oxygen fugacity and metal content of the magma according to above four determination conditions, the porphyries have a contribution of a mantle-derived material, and have excellent copper metallogenic potential, the porphyries are capable of being determined as a copper metallogenic rock mass, and a possibility of finding copper is greater than 80%, a prospecting target region is delineated within a certain radius according to an exposure position of the porphyry; and otherwise the porphyries are a non-metallogenic rock mass having small prospecting potential, and a target region is not delineated.   
     
     
         2 . The method according to  claim 1 , wherein the major elements comprise Si, Al, Fe, Mg, Mn, Fe 2+ , Fe 3+ , Ca, Na, K, P and F.